1. Field of the Invention
The field of the invention relates to optoelectronic devices generally, and more particularly to certain new and useful advances in the manufacture of encapsulated optoelectronic devices.
2. Description of Related Art
Optoelectronic devices generally comprise light emitting devices and photovoltaic devices. Both types of optoelectronic devices comprise an active layer sandwiched between two electrodes, at least one of which is usually transparent in a light emitting device, a voltage applied between the two electrodes generates electrical current through the active layer, which causes the active layer to emit light. In a photovoltaic device, such as a solar cell, the active layer absorbs energy from light and converts this absorbed energy to electrical energy, which is evidenced as a voltage and/or a current between the two electrodes.
The active layer is either an inorganic or organic electroluminescent material. One type of popular and useful light emitting device is the organic light emitting diode (OLED). Similar to inorganic light emitting diodes (LEDs), OLEDs are also a form of solid state lighting that offer high efficiencies and long lifetimes. An OLED is typically a thin-film structure formed on a substrate comprising glass or transparent plastic. This thin-film structure comprises at least the three layers described above, and may further comprise optional semiconductor layers formed adjacent the active layer. These semiconductor layers may be incorporated to facilitate the injection and transport of holes (positive charge) or electrons (negative charge).
Glass substrates offer transparency and extremely low permeability to oxygen, water vapor and/or other reactive species, which can cause corrosion and/or degradation of the optoelectronic device; but are typically not suitable for applications where flexibility is required. Plastic substrates offer flexibility and the potential for low cost roll-to-roll production, but typically have a high permeability to oxygen, water vapor and/or other reactive species. Accordingly, OLED devices comprising plastic substrates are typically encapsulated with one or more layers of barrier films that block oxygen, water vapor and/or other reactive species. The composition and methods of making conventional ultra-high barrier (UHB) films, or UHBs, are described in U.S. Pat. No. 7,015,640 and U.S. Pat. No. 7,397,183, both assigned to the General Electric Company.
Many optoelectronic functional materials that are currently used are extremely sensitive to oxygen and moisture, and it is therefore necessary to hermetically seal the devices under an inert environment. This is typically done in a dry box, with purified nitrogen or argon as the working gas. It is preferable to have oxygen and moisture contents below 110 parts per million during the encapsulation process, although this is not deemed to be limiting.
OLEDs, their barrier films and/or backsheets can be damaged in conventional roll-to-roll manufacturing. This is of particular concern for the barrier film that is used to hermetically seal the OLED, as damage induced during a roll-to-roll process may cause defects concomitant with an increased permeability of the films. This will result in a decreased shelf life of the encapsulated device. For example, FIG. 1 illustrates bi-directional compressive forces 13 and 14 that are applied during a conventional roll fabrication process to a conventional OLED device 10 that is sandwiched between a UHB 11 and a backsheet 12. The compressive forces 13 and 14 are exerted on the UHB 11 and the backsheet 12 towards the OLED device 10 by opposing, parallel rollers (not shown) of a conventional roll laminator. This causes the UHB 11 and/or the backsheet 12 to deform to create an edge seal around the OLED device 10. However, deformation of the UHB 11 around the perimeter of the OLED device 10 can create stress areas 15. Over time, portions of these stress areas 15 may exhibit cracking of the UHB 11 and/or loss of its barrier properties. Thus, there is a need for an improved thin flexible packaging technology for expanded application of low cost production of encapsulated optoelectronic devices.
Currently, manufacturing capabilities and material property limitations constrain the size of individual organic light emitting devices (OLEDs) to a relatively small dimension. By relatively small dimension is meant an area on the order of centimeters squared, when contrasted with a large area lighting panel greater than this on the order of feet squared or meter squared. Therefore, in order to obtain large area lighting panels, individual OLEDs need to be tiled together to form the larger product.
Also needed are new tiling and encapsulation equipment and processes that do not diminish OLED performance, and can produce large-area lighting products within a relatively short cycle time.